Implement tracing of mojo sync response parameters

Add support for tracing of mojo sync response parameters in
auto-generated methods. Thus provide more information for the developers
who are debugging.

Bug: 1103623
Change-Id: Ie0edadbe6007f0156d4c291775dba2e8777a2ed9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2332819
Commit-Queue: Karel Král <karelkral@google.com>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797263}

mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl

@@ -122,7 +122,8 @@ bool {{proxy_name}}::{{method.name}}(
 {%-     set qualified_method_name = "%s::%s::%s" % (namespace_as_string,
                                                     class_name, method.name) %}
   {{interface_macros.trace_event("param_", method.parameters,
-                                 qualified_method_name)}}
+                                 qualified_method_name,
+                                 trace_event_type='_BEGIN')}}
 #endif
   const bool kExpectsResponse = true;
   const bool kIsSync = true;
@@ -133,13 +134,13 @@ bool {{proxy_name}}::{{method.name}}(
 {%-     for param in method.parameters -%}
       , std::move(param_{{param.name}})
 {%-     endfor %});
-{%-   else %}
+{%-   else %}  {#- if method|method_supports_lazy_serialization #}
   {{interface_macros.build_message_flags(False, "kIsSync", "kExpectsResponse",
                                          "kFlags")}}
   {{interface_macros.build_serialized_message(
       message_name, "param_%s", params_struct, params_description, "kFlags",
       "message")}}
-{%-   endif %}
+{%-   endif %}  {#- if method|method_supports_lazy_serialization #}
 
 #if defined(ENABLE_IPC_FUZZER)
   message.set_interface_name({{class_name}}::Name_);
@@ -154,10 +155,15 @@ bool {{proxy_name}}::{{method.name}}(
           , out_param_{{param.name}}
 {%-     endfor %}));
   ignore_result(receiver_->AcceptWithResponder(&message, std::move(responder)));
-  // TODO(karelkral) Trace the out_ parameters here
+#if BUILDFLAG(MOJO_TRACE_ENABLED)
+  {{interface_macros.trace_event("out_param_", method.response_parameters,
+                                 qualified_method_name,
+                                 trace_event_type='_END',
+                                 dereference_parameters=True)}}
+#endif
   return result;
 }
-{%-   endif %}
+{%-   endif %}  {#- if method.sync #}
 
 void {{proxy_name}}::{{method.name}}(
     {{interface_macros.declare_request_params("in_", method)}}) {

mojo/public/tools/bindings/generators/cpp_templates/interface_macros.tmpl

@@ -24,29 +24,59 @@ base::OnceCallback<void(
 {%-   endif -%}
 {%- endmacro -%}
 
-{%- macro trace_event(prefix, method_parameters, qualified_method_name) -%}
+{%- macro trace_event(prefix, method_parameters, qualified_method_name,
+                      trace_event_type='', dereference_parameters=False) -%}
 {#- This macro assumes that the argument names are the ones declared by -#}
-{#- |declare_request_params|. Namely the |prefix| should be the same here as -#}
-{#- in |declare_request_params|. -#}
+{#- |declare_request_params/declare_sync_method_params|. Namely the |prefix| -#}
+{#- must be the same here as in -#}
+{#- |declare_request_params/declare_sync_method_params|. -#}
+{#- |trace_event_type| can be set to: -#}
+{#-   '' just standalone trace. -#}
+{#-     Parameter names must match |declare_request_params|. -#}
+{#-   '_BEGIN' input parameters to be later merged, must be before the _END. -#}
+{#-     Parameter names must match |declare_request_params|. -#}
+{#-   '_END' merge corresponding sync response parameters. -#}
+{#-     Parameter names must match |declare_sync_method_params|. -#}
+{#- |dereference_parameters| the parameters type is actually |kind*|. -#}
 {%-   if method_parameters -%}
-  TRACE_EVENT1(
-    "mojom", "{{qualified_method_name}}", "input_parameters",
+  TRACE_EVENT{{trace_event_type}}1(
+{%-     if trace_event_type=='' or trace_event_type=='_BEGIN' -%}
+{%-       set parameter_group = 'input_parameters' -%}
+{%-     else -%}
+{%-       set parameter_group = 'response_parameters' -%}
+{%-     endif  %}
+    "mojom", "{{qualified_method_name}}", "{{parameter_group}}",
     [&](){
       auto value = std::make_unique<base::trace_event::TracedValue>();
       base::trace_event::TracedValue* raw_value = value.get();
 {%-     for param in method_parameters %}
-{%-       for line in param.kind|write_input_param_for_tracing(
-                                   parameter_name=param.name,
-                                   cpp_parameter_name=prefix+param.name,
-                                   value='raw_value') %}
+{%-       if dereference_parameters -%}
+{%-         set cpp_parameter_ptr = prefix + param.name %}
+{%-         set cpp_parameter_name = "(*%s)" % cpp_parameter_ptr %}
+      if ({{cpp_parameter_ptr}}) {
+{%-         for line in param.kind|write_input_param_for_tracing(
+                                     parameter_name=param.name,
+                                     cpp_parameter_name=cpp_parameter_name,
+                                     value='raw_value') %}
+        {{line}}
+{%-         endfor %}
+      } else {
+        raw_value->SetString("{{param.name}}", "nullptr");
+      }
+{%-       else %}  {#- if dereference_parameters #}
+{%-         for line in param.kind|write_input_param_for_tracing(
+                                     parameter_name=param.name,
+                                     cpp_parameter_name=prefix+param.name,
+                                     value='raw_value') %}
       {{line}}
-{%-       endfor -%}
+{%-         endfor %}
+{%-       endif  %}  {#- if dereference_parameters #}
 {%-     endfor %}
       return value;
     }());
-{%-   else -%}
-  TRACE_EVENT0("mojom", "{{qualified_method_name}}");
-{%-   endif %}
+{%-   else -%}  {#- if method_parameters -#}
+  TRACE_EVENT{{trace_event_type}}0("mojom", "{{qualified_method_name}}");
+{%-   endif %}  {#- if method_parameters #}
 {%- endmacro -%}
 
 {%- macro declare_sync_method_params(prefix, method) -%}